1. Field of the Invention
The present invention relates to the production, composition and use of fertilizer granules or pellets in which inorganic nutrients have been thoroughly and exceptionally incorporated into sewage sludge so as to become a homogeneous mix. The composition of mixed sludge and nutrients can be used as an enriched fertilizer product in the form of wet cake after mixing, or after granulation and/or drying. The process of the invention is intended to produce a product in which the inorganic nutrients are virtually indistinguishable from the sludge into which they have been incorporated. The invention includes the incorporation of nitrogen, phosphorus and potassium nutrient compounds and other nutrients into sewage sludge by premixing them with the sludge prior to use or further processing for the purpose of changing the final, physical form of the product by granulation or drying.
The use of products derived from sewage sludge as a fertilizer has been in practice for years. The organic matter in the solids, particularly the organic nitrogen compounds are in a matrix that provides for the slow release of the inherent nutrients into the soil. Previously, fertilizer producers have also been mixing a variety of inorganic nutrient materials to tailor the nitrogen, phosphorus, potassium (NPK) to meet the needs of specific crops or land applications. The challenge for this industry has been the inability to produce a thoroughly mixed, uniform material that will maintain its NPK assays at all stages of production, handling and application. The science of bulk solids flow properties largely expects segregation and separation of materials, when materials of various sizes and densities are mixed together. For fertilizer products, the challenge is compounded by the sheer volume of material that is mixed, transported and applied.
2. Description of Related Art
Older technologies include U.S. Pat. No. 6,841,515 (Jan. 11, 2005) which concerns a fertilizer core particle with one or more concentric layers that are distinguishable from the core with respect to nutrient content, density, hardness, etc. U.S. Pat. No. 7,513,927 (Apr. 7, 2009) relates to a fertilizer product that prevents self heating but is primarily concerned with the in situ formation of ammonium sulfate. The focus of this patent is on “enriched inorganic fertilizer” wherein biosolids are placed into inorganics, in contrast to the present invention wherein inorganics are incorporated into biosolids.
Accordingly, the product of the present invention is homogeneous enriched biosolids fertilizer. The inventors have informally referred to the product as “Bioblend.”